Zein solution and coating composition



Patented Dec. 2c, 1939 PATENT orncs ZEIN SOLUTION AND COATINGCOMPOSITION Roy E. Coleman. Chicago, 111., minor to The zein Corporationof America, a corporation of Delaware No Drawing. Original applicationSeptember e1,

1939, Serial No. 295,919. Divided and this applicatlon October 11 1989,Serial No. 298,987

I 8 Claims. This invention relates to improvements in substantiallyanhydrous solutions and coating compositions of zein and to methods ofpreparing the same. While the present invention is applicable to theproduction of solutions and coating compositions of other prolamins'. itis particularly directed to securing substantially anhydrous solutionsand coating compositions of zein with controlled solution gellingcharacter- 10 istics, zein being diiferentiated from other prolamins byits unusual gelling tendencies.

This application is a division of my prior copending application SerialNo. 295,919, filed Sept. 21, 1939.

The solutions and coating compositions of my present invention arecharacterized by the fact that they contain either no added water oronly very slight amounts of water not in excess of about 5% and are,therefore, substantially anhydrous.

The zein used in accordance'with my invention may be the commercial zeinwhich contains a small percentage of moisture in the order of about 5 toabout 8%, preferably about 8%, and is obtained in the trade in powderedform, or it may be a specially treated substantially anhydrous zein. Inthe following description of my invention I refer by the term zein" tocommercial zein or to' zein of substantially the water content ofcommercial zein unless otherwise specifically designated.

In the prior art zein coating compositions, water has been included to asubstantial extent, t being considered that the solubilitycharacteristics of zein required the inclusion of substantialproportions of water in organic solvents. Forexample, as stated in thewalsh et al. Patent No. 1,966,604,- the addition of water is necessarysince the low-molecular weight alcohols, alcohol ethers 40 andalcohol'derivatives are not eflective alone in making solutions of zein.

In accordance with the present invention 1 have found thatnon-separating, stable liquidtion may separate and become solid;however, on heating again totemperatures of from about 45 to 70 F., are-solution is effected, either without stirring or with slightstirring, and the solutions and coatings return to their normal form 5at the re-heating temperatures.

The stable non-separating solutions and coating compositions prepared inaccordance with the present invention may be controlled as to theirgelling characteristics, as hereinafter set forth, and may be slowgelling or substantially non-gelling with slight tendency to increase inviscosity; that is, to thicken or become heavier in body; and in manyinstances they exhibit practically no tendency to thicken or to gel overpractical periods of time in the order of about 3 to about 6 months. Byvirtue of these novel stable characteristics, the solutions and coatingsof my invention are not limited to use immediately or within shortperiods of time after preparation as is generally the case with theprior art solutions and coating compositions. The solutions and coatingcompositions of the present invention generally remain stable andreasonably constant 'in their characteristics during the periodsnecessary for transportation and distribution, either in bulk or inpackages, or for storage for reasonable periods of time, and hence theirfield of applicability is greatly increased.

In accordance with the present invention, I have found that solutionsand coatings of zein having the desired non-separating, controlledgelling or non-gelling characteristics may be secured by a suitablebalance between the hydrocarbon constituents or radicals present in thesolvent or solvent mixtures and the polar constituents or radicalspresent therein, the presence of a certain proportion of carbon-bondedhydroxyl radicals being required to secure solvent action. The presenceof a hydroxyl group in a primary alcohol radical, CH2CH, appears to beparticularly helpful in securing such action. The presence-of anexcessive proportion of hydroxyl radicals or of polar radicals includingsome hydroxyl radicals causes or accelerates 5 gelling tendencies in thezein solution or coating. Polar radicals such as 0- (ether oxygen), Cl,NHz; =00 and COI-I thus appear to aid'or cooperate with OH in securingthe necessary conditions of polarity in the solvent (in which term Iinclude solvent mixtures in the present case) for solvent action, and inexcess produce the, conditions enhancing gelling. While in solutionsabsence of gelling or slowgelling or thickening is desirable, in theprepas5 ration of plastics rapid gelling may be desirable. In thepresent case I am more particularly concerned with solutions havingslow-gelling'or substantially non-gelling characteristics for use incoating compositions; i. e. solutions which do not gel or which gel orthicken so slowly as to per-. mit normal commercial handling withoutmaterial or serious thickening or gelling.

The proportion of hydrocarbon or non-polar radicals in the solvent orsolvent mixture should not be excessive, since too high a proportion ofhydrocarbon apparently causes insolubility and separation of the zein.The same is the case in the presence of excessivly long or largehydrocarbon radicals; e. g. C; and higher alkyl radicals. Cyclichydrocarbon radicals, however, behave as lower alkyl radicals. Thus, aswill appear hereinafter, the benzyl radical acts as if it wereintermediate between the methyl and ethyl radicals. This is consistentwith the polar characteristics of aryl-alkyl radicals as compared withalkylalkyl radicals.

The desired balance of polar constituent radicals and hydrocarbon ornon-polar radicals in the solvent may be secured by the use of asuitable individual compound which inherently has the necessary balance,or by an admixture of compounds which are individually not balanced tosecure proper relations in the mixture and which individually may-not besolvents for zein. The behavior of such mixtures may be explained byassuming solvation of the zein molecules or micelles by the hydroxylatedconstituents of the mixture, with orientation of the hydrocarbonradicals of the hydroxylated compound to the exterior of the solvatecomplex, which may then disperse or dissolve in the remainingconstituents of the solvent.

The proportion of polar radicals to hydrocarbon or non-polar radicalswhich I have found to be desirable lies within a range which extendsbetween the limits of absolute methanol on the one hand, having 53%hydroxyl and 47% hydrocarbon, and absolute ethanol on the other handhaving 37% hydroxyl and 63% hydrocarbon. This range is approximate andmay vary somewhat depending on the solvent or solvent mixture used. Thelimits of this range are, however, indicative of gelling characteristicson the one hand and of insolubility on the other and, therefore,provides a close and adequate guide to enable the operator, by simpleexperimentation, to determine the required balance of polar andhydrocarbon radicals to effect solution of zein in any solvent ormixture of solvents of a character herein set forth. Thus absolutemethanol has decided solvent action but has excessive gellingtendencies, as has also ethylene glycol, which has an even higherproportion of OH than has methanol. Glycerol, also higher in OH thanmethanol, shows no appreciable solvent action on zein, a behavior whichis probably related to its high surface tension. On the other hand,absolute ethanol, isopropanol, and higher alcohols have no apparentsolvent action.

It is, of course, obvious that certainsolvents or mixtures of solventshaving a balance of polar and hydrocarbon radicals within the limitsabove set forth will produce solutions or coatings which are moresuitable for special commercial purposes than other balanced solvents orbalanced mixtures of solvents. By using the critical polar-hydrocarbonradical balance range as a guide, it is possible, by simpleexperimentation, to determine readily that particular balanced solventor balanced mixture of solvents which. i

.will .produce the solution or coating composition having the desiredproperties and characteristics for the special purpose;

Various relatively high molecular weight alcohols, having a ratio ofpolar to non-polar radicals between methanol and ethanol are excellentindividual solvents for'zein with the production of non-gelling,non-separating solutions and coatings, as set forth in my priorapplications Serial No. 187,559,*Serial No. 187,560, and Serial No.188,182, which were filed as contlnuations-. in-part of applicationSerial No. 158,215. The solvents of these applications includediethylene glycol, 'triethylene glycol, propylene glycol, diacetonealcohol, benzyl alcohol, cyclo-hexanol and furfuryl alcohol, as well astetrahydrofurfuryl alcohol, and the like. These'solvents are capable ofdissolving zein to producesolutions or coating compositions which arestable against separation and are controlled to be slow-gelling orsubstantially non-gelling over practical periods of time; in many casesover from about 3 "to about 6 months. In Examples 1 to 8 of my priorapplication Serial No. 295,919, I disclose methods of preparing zeinsolutions by the aid of these individual solvents.

Considering the cyclic and aryl-alkyl radicals of the compounds benzylalcohol, cyclohexanol, furfuryl and tetrahydrofurfuryl alcohols, forexample, as intermediate between the CH3- and,

the CHaCHz radicals, it will be noted that in all of these solvents theproportion of polar radicals (OH or OH and O) may be re-- garded as ifit were intermediate between the ratios for methanol and ethanol. I havefound that any of the above balanced solvents or mixtures of them may beused in or added to other solvents or solvent mixtures, otherwisebalanced or approximately balanced, such additions being frequentlydesirable. Thus, benzyl alcohol aids in securing a bright clear zeinfilm. In general,

also, these solvents may be used with various proportions of ethanol,glycol or the like, providing the ratio of hydroxyl and other polargroups to hydrocarbon radicals is maintained within the proper balance,as set forth in Examples 9 to 24 of my application Serial No.

hydroxyl or polar radicals with compound hav-- ing a balance or anexcess thereof to secure the desired balance of polar and hydrocarbonradicals in the resulting mixtures. An extreme example of the productionof such solvents is the admixture of toluene (a non-solvent for zein)and methanol. Mixtures of methanol and toluol containing 5 to 45% oftoluol are excellent solvents for zein, and have retarded .and in somecases relatively slow-gelling tendencies. The preferred range is 35 to45% toluol. Examples 30 to 34 of my prior application Serial No.295,919are illustrative of such mixtures.

Anhydrous or substantially anhydrous solvents may be prepared fromthealiphatic alcohols having from 2 to 4 carbon atoms by adding theretohydroxylated or polar compounds having higher ratios of OH or polargroups (including CO, NHa, O or OH) then ethanol to secure the desiredbalanced relations between polar and non-polar groups. The simplestmonoand polyhydric alcohols are particularly useful in this connection,these being methanol, glycol I and glycerol. Examples to 41 of my priorap- .plicati n Serial No. 295,919 are illustrative of zein s tures.

Solvent mixtures of non-gelling or controlled gelling characteristics inaccordance with the utions prepared with such solvent mixpresentinvention may be produced by mixing and of furfuryl alcohol. On stirringand with the application of heat in the order of 190 so .to 200 F., anon-separating, substantially nongelling stable solution of the zein inthe solvent mixture is obtained in about 10 to 15 minutes.

Example 2 10 parts of zein are mixed with 30 parts of propylene glycoland 10 parts of benzyl alcohol in a suitable vessel. On stirring andwith the application of heat in the order of about 1'70 to 185 F., anon-separating, substantially non-gelling stable solution of the zein inthe solvent is obtained in about 10 to 15 minutes.

Example 3 Example 4 10 parts of zein are mixed with 10 parts ofdiacetone alcohol and 30, parts of diethylene glycol in a suitablevessel. On stirring and with the application of heat in the order ofabout to F., a non-separating, substantially non-gelling stable solutionof the ze'n in the solvent mixture is obtained in about 10 to 15minutes.

Example 5 10 parts of zein are mixed with 30 parts of furfuryl alcoholand 20 parts of propylene glycol in a suitable vessel. On stirring andwith the application of heat inthe order of about 1'75 to R, anon-separating, substantially non-gelling stable solution of the zein inthe solvent mixture is obtained in about 5 to 10 minutes.

The solvents and solvent mixtures for zein set forth above and theresulting solutions prepared in accordance with the present inventionare substantially anhydrous, containing not more than 5% of added waterand, preferably, substantially less. The proportions of waterpermissible are thus limited in order to secure the desired solutioncharacteristics and control of gelling, since'it has been found that thepresence of water in excess of the proportions above indicated disturbsthe balance of the solvent, tending to produce or to accelerate gelling,as well as to impair the character of the zein film deposited from thesolution. Possible explanations of the behavior of water may be made onthe basis that it acts as a highly polar constituent when present insolution in excess, that it tends to cause solvation or hydration of thezein, and its tendency to cause gelling may also be related ,to its highsurface tension. The permissible proportion may vary in various solventsor solvent mixtures, the maximum permissible being represented by thepermissible proportion of 5% in the case of ethyl alcohol or the ethylalcohol constituent of the solvent. Since ethyl alcohol with 5% water isa solvent producing stable solution in only limited cases, as set forthin my application Serial No. 158,215, 'andin all other -instanees is butone constituent of-a mixture,

it will be apparent that the solventsprepared in accordance with thepresent invention contain (except in those specific instances)substantially less than 5% of added water.

' Theextent of the effect of water and the permissible proportionthereof varies with the solventor solvent mixture and, in general, themore closely the solvent or solvent mixture approaches the desiredbalance of polar groups and hydrocarbon constitutents, the less thepermissible proportion of water to avoid the introduction of excessivegelling or insolubility. In some cases small proportions of water belowthe limits above set forth may be advantageous. The maximum permissibleproportion may be readily determined experimentally in each instance andin many cases may be as low as 2 or 3%.

By the term substantially anhydrous, in connection with solvents orsolvent mixtures, as used herein, I mean having insufficient water inthe solvent or solvent mixture to disturb the balance thereof andintroduce excessive gelling or insolubility; and having in no case morethan 5% of water.

By the use of anhydrous or substantially anhydrous solvents or solventmixtures in accordance with my invention, I ,am thus enabled to preparesubstantially non-aqueous zein solutions and coating compositions whichcontain no added 7 drawbacks as to brittleness, lack of luster and glossand blooming and blushing tendencies of the films deposited from theaqueous solutions or coating compositions of the prior art.

Certain anhydrous or substantially anhydrous compounds or mixtures ofcompounds in accordance with my invention, characterized in, having abalance of polar and hydrocarbon radicals approaching that of ethanoland bordering the desired range, have been found to be excellentsolether, diethylene glycol monomthyl ether, ethylene glycol monoethylether, diethylene glycol monoethyl ether and'llke alcohol-ether solventsor mixtures thereof. Examples 42 to 44 of my By virtue of priorapplication Serial No. 295,919 are illustrative of solutions preparedwith these-solvents.

parts by weight of the solvent to one part byweight of the zein has beenfound sufficient to dissolve the zein and form the desired stablesolutions or coating compositions. The viscosity and gelling tendenciesof the solutions or coating compositions prepared in accordance, with myinvention are at least in part dependent on the proportion of solventused.

The coating compositions embodying my invention have the unusualproperties, particularly when heated, of being able to give up theirsolvent or sol-ventsreadily when applied to any surface to quickly andreadily form tough, flexible, non-tacky, hard and generally transparent.

films even when retaining some solvent. The films deposited from coatingcompositions in accordance with my invention are very strong and haveunusual adherent properties. In these coating compositions the filmforming properties thereof can be built up to produce a film of greatertoughness, flexibility, hardness and gloss than is capable of beingformed from coating compositions containing added water in an amountgreater than as in the prior art. Under normal temperature conditions,the solutions or coating compositions in accordance with my inventionwill produce non-blushing coatings on drying, without the aid ofsupplementary anti-blushing agents as in the prior art.

The coating compositions in accordance with my invention may be appliedto any surface and they may be used for coating, sizing, or impregnatingany material, such as paper, textiles, wood, wood pulp and the like.When coated on paper, Cellophane, glass and the like, a film is formedalmost immediately which possesses the film characteristics set forthabove. Since these coating compositions have decided adhesiveproperties, they may be used either per se or in combination with othermaterials for uniting or laminating paper, cloth, wood, glass, felt,Cellophane, metals and metal foils and the lik The characteristics ofthe coating compositions in accordance with my invention, and hence ofthe ultimate films formed therefrom, can be altered at will and asdesired by the inclusion of diluents, modifiers, plasticizers, resins,cellulose derivatives, fillers and the like all as set forth in my priorapplication Serial No. 295,919.

I claim:

1. A substantially non-aqueous liquid coating composition comprising asolution of zein in a substantially anhydrous mixture of solventscomprising a plurality \oforganic compounds each having a proportion ofpolar to non-polar radicals which lies within a range extending betweenthe limits of the proportion of polar to non-polar radicals of methanoland the proportion of polar to non-polar radicals of ethanol, saidsolvents and said composition containing less than 5% of added water,and said composition being stable against separation of the zein attemperatures of 70 F. and being substantially non-gelling.

2. A substantially non-aqueous liquid coating composition comprising asolution of zein in a substantially anhydrous mixture of solventshavwhich lies within a range extending between the limits of theproportion of polar to non-polar proportion of polar .to non-polarradicals of ethanol, said mixture of solvents comprising a plurality oforganic comradicals of methanol and the pounds each having a proportionof polar to non-;

polar radicals which lies within a. range extending between the limitsof the proportion of polar to non-polar radicals of methanol and thepropor-' tion of polar to non-polar radicals of-ethanol, said solventsand said composition containing less than 5% of added water, and saidcomposition being stable against separation of the zein at temperaturesof 70 F. and being substantially non-gelling.

3. A substantially non-aqueous liquid coating composition comprising asolution of a prolamin in a substantially anhydrous mixture of solventshaving a. proportion of polar to non-polar radicals which lies within arange extending between the limits of "the proportion of polar to non-.

polar radicals of methanol and the proportion of polar to non-polarradicals of ethanol, said mixture of solvents comprising a plurality oforganic compounds each having a' proportion of polar to non-polarradicals which lies within a range extending between the limits of theproportion of ing a proportion of polar to non-polar radicals polar tonon-polar radicals of methanol and the proportion of polar to non-polarradicals of ethanol, said solvents and. said composition containing lessthan 5% of added water, and said composition being stable againstseparation of the prolamin at temperatures of 70 F. and be ingsubstantially non-gelling.

4. A substantially non-aqueous liquid coating composition comprising asolution of zein in a substantially anhydrous mixture of solvents having a proportion of polar to non-polar radicals which lies within arange extending between the limits of the proportion of polar tonon-polar radicals of methanol and the proportion of polar to non-polarradicals of ethanol, said mixture of solvents comprising berizyl alcoholand a glycol having a molecular weight higher than ethylene 1 glycol,said solvents and said composition containing less than 5% of addedwater, and said composition being stable against separation of the zeinat temperatures of 70 F. and being substantially non-gelling.

5. A substantially non-aqueous liquid coating composition comprising asolution of zein in a substantially anhydrous mixture of solvents having a proportion of polar to non-polar radicals which lies within arange extending between the limits of the proportion of polar tonon-polar which lies within a range extending between the limits of theproportion of polar to non-polar radicals of methanol and the proportionof polar to non-polar radicals of ethanol, said mixture of solventscomprising benzyl alcohol and furiuryl alcohol, said solvents and saidcomposition containingless than 5% of added water, and said compositionbeing stable against separation of -65 radicals of methanol and theproportion of polar I the zein at temperatures of 70 F. and {beingsubstantially non-gelling.

7. A substantially non-aqueous liquid coating composition comprising asolution of zeln in a substantially anhydrous mixture of solvents havinga proportion of polar to non-polar radicals which lies within a rangeextending between the limits of the proportion df polar to non-polarradicals of methanol and the proportion of polar to non-polar radicalsof ethanol, said mixture of solvents comprising cyclohexanol andtriethylene glycol,- said solvents and saidpomposition containing lessthan 5% of added water, and said composition being stable againstseparation of the zeln at temperatures of 70 F. and being substantiallynon-gelling.

8. The method' of preparing a substantially non-aqueous zeln solutioncontaining not in excess of 5% of added water which is stable againstseparation of the zeln at temperatures of 70 F. and which is relativelynon-gelling, comprising dissolving zeln in a substantially anhydrousmixture of solvents comprising a plurality of organic compounds eachhaving a proportion of polar to non-polar radicals which lies within arange extending between the limits of the proportion of polar tonon-polar radicals of methanol and the proportion of polar to non-polarradicals of ethanol, said solvents containing less than 5% of water.

ROY E. COLEMAN.

